To detect a rotational speed of a shaft, or more generally the rotational speed of a rotating body, for example an engine speed, e.g., at a crankshaft, sensor systems are known which have a material measure which is situated circumferentially around the rotating body and is referred to as a phase track, in the form of a sequence of repeating, periodic markings, as well as at least one sensor element which is situated fixed in place opposite the rotating body and which detects the phase track. The sensor element is sensitive to the markings of the phase track and generates a sensor signal, for example when passing a marking and/or when adjacent markings are changed, so that a known number or a known sequence of sensor signals is/are generated over a determined rotation angle, e.g., over one full rotation, a rotational speed being ascertained or inferred from the sensor signals with the aid of an evaluating unit by involving a time signal.
The markings of the phase track may be, for example, optical markings, so that the sensor element may detect, for example, light/dark transitions. Other sensor principles, such as magnetic or capacitive principles, are also possible for the same purpose.
The phase track may be situated directly on the rotating body or on an element which is non-twistably connected thereto, such as a sensor wheel, for example.
Hall elements, for example, may be used as sensor elements, the markings of the phase track having a magnetic configuration, for example as a sequence of alternating magnetic north and south poles. In addition to Hall elements, the use of magnetoresistive elements, for example GMR elements (GMR=giant magnetoresistor) are also known.
In the case of the sensor wheels, so-called multipole sensor wheels are known which are made of a material capable of magnetization. In this regard, the markings of the phase track are magnetized as magnetic north and south poles which are alternatingly situated in the circumferential direction, similarly to the teeth of a toothed wheel, a so-called steel sensor wheel, as described above. Methods are known, for example, for manufacturing and magnetizing a sensor wheel from a homogeneous, ferromagnetic material, e.g., from steel, as well as for using a plastic-bonded, magnetizable material in the manufacture of sensor wheels.
If Hall elements are used as sensor elements, for example, a differential evaluation may take place, the difference between the signals of two Hall elements situated consecutively in the circumferential direction being evaluated. So-called Hall ASICs are also known per se, which are able to evaluate a magnetic field direction. Furthermore, the use of two-channel, differential Hall element configurations in the form of so-called dual differential sensor elements are known, which may be used to detect both the rotational speed and the direction of rotation. These Hall element configurations include a total of three sensor elements, each of two sensor elements being interconnected to form antiparallel-connected sensor element bridges. Both sensor element bridges extend parallel to the direction of rotation of the phase track, which, in a top view, runs perpendicularly to the rotation axis.
Furthermore, for example, EP 1 861 681 B1 refers to circumferentially situating a phase track at least on two cross sections of a rotating body of known torsional stiffness, which are located at a known distance from each other in the axial direction along a rotation axis, for the purpose of determining a torque transmitted between the two cross sections of the rotating body by determining a torsion angle between the two cross sections and inferring the torque present between the two cross sections on the basis thereof, via the torsional stiffness. It is apparent that the torsion angle is the torsion and the torque is the attacking torsional moment.
Also, EP 1 861 681 B1 indicates that when detecting a rotation angle of a rotating body, compensating for a tilting between the sensor track provided by the optimum detection or resolution of the passing of markings on the sensor element and direction of rotation of the phase track which, in a top view, runs perpendicularly to the rotation axis, by using multiple phase tracks which are circumferentially situated parallel to each other, and a matrix-based evaluation of all phase tracks.